This invention relates generally to apparatus for use with extra-corporeal blood passing equipment, and more particularly concerns the control of blood flow in both withdrawal and return directions between a single blood vessel cannula and the equipment. The present invention employs a novel method and design to substantially reduce dead space volume in the hub of the needle. It also includes other features enabling improved usage as a needle for single needle dialysis, two needle dialysis, monitoring pressure, intravenous administration, drug injection and blood sampling.
The phenomenon termed "recirculation", as used in and associated with single needle hemodialysis, is caused by two contributing factors, i.e. (a) the amount of dialysed blood which is withdrawn from the blood vessel back into the extracorporeal withdrawal circuit, without fully being mixed with the patient's undialysed (uncleansed) blood, and (b) the amount of dialysed blood which is withdrawn out of the needle hub back into the extra-corporeal (withdrawal) circuit.
The first factor is relative and is mostly determined by the pressure gradient (difference) between the pressure in the extra-corporeal blood circuit and the blood vessel pressure. The latter is constant or remains constant as it is determined by the dead space volume of the blood remaining in the hub of the needle, i.e. the greater the dead space and ease of shunting of blood from the infusion side to the withdrawal side, the greater the recirculation and the less efficient the treatment. Conversely, the smaller the dead space and the less tendency for shunting of blood, the less blood recirculated and the more efficient the treatment.
Recirculation in single needle hemodialysis remains as the key disadvantage to continued widespread use of the therapy. Prior art systems and needles have not been able to further reduce this percentage amount of recirculation of blood in order to cause the efficiency of treatment of single needle hemodialysis to be close to that of two needle dialysis. It is true, as previously acknowledged by others skilled in the art that the ability to maximize the stroke volume, i.e. the amount of blood pumped in each alternating cycle, reduces the amount of blood recirculated by decreasing the percentage difference; however, it does not eliminate recirculation by itself.
There is need for rapidly installable and efficiently operable apparatus for controlling the flow of blood between a patient's vessel or vessels and extra-corporeal means such as dialysis equipment. In this regard, it is highly desirable that cannulation and dialysis be carried out with minimum disturbance to the patient, and with equipment that enables efficient and optimized control and monitoring of vessel penetration, blood flow and infusion of other solutions. Prior apparatus of which I am aware does not incorporate the unusually advantageous features of construction, modes of operation and surprisingly favorable results afforded by the invention, as will appear.